1. Field of the Invention
The invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device and driving method.
2. Description of the Related Art
Liquid crystal display devices, with the characteristics of higher pixel resolution, higher display quality, lighter weights, thinner sizes, lower operation voltage, as well as low power consumption, are used in a wide variety of commercial applications, including cell-phones and digital cameras for small screen display panels, and large screen televisions exceeding 40 inches.
The liquid crystal display devices have the common feature of consisting of two (a pair of) substrates with one transparent glass substrate at least, sandwiching a liquid crystal material therebetween. The transmittance/interception of light is relative to the direction of the liquid crystal with a voltage applying thereto. The light transmitting/blocking state of a specific pixel is corresponding to a selective voltage applied across the transparent conductive layer (between the pixel electrode formed on the thin-film transistor (TFT) substrate module and the opposite electrode formed on the other substrate module) on the two substrate-models of the liquid crystal display panels.
Research and development focusing on liquid crystal display devices having lighter weights, thinner sizes, lower operation voltage, low power consumption, and display quality improvement have been undertaken to displace cathode-ray tube (CRT) as the most commonly used display device. Recent developments have led to the development of liquid crystal material and the improvement of a driving method thereof, which can meet high quality display requirements.
The cathode-ray tube uses an impulse-type light illumination by scanning of an electron gun, while the liquid crystal display device uses a hold-type light illumination with a plurality of linear lamps, such as fluorescent lamps, behind the liquid crystal display panel, resulting in sub par display performance for moving images as compared to the cathode-ray tube.
Because human eyes have integration time, blur phenomenon occurs when eyes focus on light emitted from a specific position of an object in the image projected onto the retina of the eye during a frame period. The contour of a moving object trailing an afterimage may be perceived in accordance with the mismatch phenomenon of the movement due to the motion blur effect.
Thus, displaying for a hold-type liquid crystal display device results in motion blur with respect to the aforementioned contour blur or called contour aliasing. Additionally, the animation quality deteriorates due to the ghost phenomenon caused by the interpolated position between the image of the preceding and succeeding frames. Such that the phenomenon of motion blurs and ghosts are generally referred to as edge-blurs.
Recently, research has led to reducing edge-blur and improving the display quality of animation for liquid crystal display devices as Jpn. Pat. Appln. Kokai Publication No. 11-202286.
FIGS. 1 and 2 are block diagrams, with FIG. 1 illustrating a liquid crystal display device for improving the display quality of animation by dividing a plurality of luminescent regions along the display of the vertical scan and FIG. 2 illustrating an illumination unit in FIG. 1 disclosed in patent reference 1.
As shown in FIG. 1, the liquid crystal display device comprises a liquid crystal display panel 100, a driving unit 200, a backlight unit 300, an inverter circuit 400, and a display control device 500. The driving unit 200 drives each pixel arranged in a matrix on the liquid crystal display panel 100. The backlight unit 300 in the back of the liquid crystal display panel 100 is divided into a plurality of luminescent regions, for instance, four regions in FIG. 1, 310, 320, 330, and 340, and installing fluorescent lamps 311, 321, 331, and 341, respectively. The inverter circuit 400 individually turns on/off the plurality of fluorescent lamps 311, 321, 331, and 341. The display control device 500 controls the driving unit 200 and the inverter circuit 400.
The backlight module is used as the backlight unit 300 of the liquid crystal display panel 100. The plurality of luminescent regions 310, 320, 330 and 340 are divided into a plurality of strip regions for the direction of vertical scanning. The fluorescent lamps 311, 321, 331, and 341 in each luminescent region individually illuminate the region where the liquid crystal display panel corresponds to the luminescent regions. In addition, a lamp reflector 350 disposed inside the backlight unit 300 for reflecting the light from a fluorescent lamp to the liquid crystal display panel 100, and an optical sheet 360 is disposed on the backlight unit 300 for uniform the light
The image-writing signal of the liquid crystal display panel 100 is inputted through the driving unit 200 from the display control device 500. In addition, lighting the fluorescent lamp disposed in each luminescent region inside the backlight unit 300 is controlled by the luminescence control signal inputted by the display control device 500 through the inverter circuit 400.
As shown in FIG. 2, the illumination unit comprises a backlight unit 300, an inverter circuit 400, a divide counter 510, and a shift register 520. The divide counter 510 and the shift register 520 are disposed in the display control device 500 shown in FIG. 1, wherein the divide counter 510 divides the scanning shift clock, and then outputs the signal of dividing frequency to the inverter circuit 400 with the shift register 520 synchronizing with the scanning timing signal.
Inverters 401, 402, 403 and 404, each respectively driving the corresponding fluorescent lamps 311, 321, 331 and 341 in each of the luminescent regions 310, 320, 330 and 340, are disposed in the inverter circuit 400. In addition, the signal of dividing frequency according to the shift register 520 is inputted to inverters 401, 402, 403 and 404 sequentially, and then, the fluorescent lamps 311, 321, 331 and 341 and sequentially turned on by the timing of delaying only for a predetermined time from the vertical signal (image-writing signal) inputted from the liquid crystal display panel.
FIG. 3 is a timing chart explanatory of the liquid crystal response for the image-writing signal, the timing of lighting the fluorescent lamps, and the visible image perceived by the liquid crystal display observers for the liquid crystal display device shown in FIG. 2. The first timing chart in FIG. 3 illustrates the frame signal, the second chart is the image-writing signal which inputted to the pixel of the nth vertical line of the liquid crystal display panel, the third chart is the liquid crystal response time regarding the image-writing signal inputted to the pixel of the nth vertical line, the fourth chart is the on/off signal of the fluorescent lamps in the luminescent regions corresponding to the pixels of the nth vertical line, and the fifth chart is the visible image perceived from the concerning pixels by the observer.
When the voltage applied to the liquid crystal changes, the direction of the liquid crystal and the brightness of the pixels are correspondingly modified. At this time, the timing of the liquid crystal response is the delay of the timing of the change in the applied voltage for a predetermined time. Therefore, the change of the brightness is perceived by the observer in the process that the liquid crystal is changed from the state of a black display to the state of a white display when the fluorescent lamp is turned on according to the same timing as the input timing of the image-writing signal of the white display signal. On the contrary, the observer distinguishes the difference of the brightness when the liquid crystal is changed from the state of a white display to the state of a black display and the fluorescent lamp is turned off according to the same timing as the input timing of the image-writing signal of the black display signal. Additionally, the change of the brightness corresponding to the liquid crystal response is regarded as a result of edge-blur of the animation.
The change process of the liquid crystal response may not be perceived by the observer if it is assumed that the way of turning on and turning off of the fluorescent lamp is periodically after a predetermined time passed from rewriting the image signal for each frame period as shown in the fourth timing chart of FIG. 3. Thereafter, the edge-blur in the animation displayed may be suppressed and the lifelike quality of the animation may be provided.
In addition, the technology for improving the characteristics of the animation by utilizing an impulse-type manner for the image display of the hold-type liquid crystal display is also provided, for example, the method of interpolating black data between frames, the blocking method of blinking the backlight during a frame period, or, the scanning backlight method of sequentially blinking the backlight by way of area light during the period of the vertical scanning in one frame.
However, it is necessary for the inverters of the related art shown in FIG. 2 to be disposed in each luminescent region for constructing circuits individually, generating the timing signals in the plurality of luminescent regions, respectively.
Moreover, it is difficult for the related art to improve upon animation quality without concerning the liquid crystal response in accord with temperature dependency, even though the liquid crystal response changes with different liquid crystal temperature.